The current invention is directed to a closure for a container. More specifically, the current invention is directed to a plastic closure having a seal adapted to withstand retorting.
Certain beverages and food stuffs, for example, liquid pediatric nutritional products, must be sterilized after being hermetically sealed in the containers in which they will ultimately be sold. Sterilization is typically accomplished by a retorting process in which the container is heated to relatively high temperatures, such as 260xc2x0 F. or above. Although steam is used to subject the container to external pressurization during retorting in order to reduce the effects of the increased internal pressure generated by the heating, there is nevertheless a pressure imbalance that imposes additional forces on the container and closure. Thus, the closures for such containers, which are typically referred to as xe2x80x9cretortable closures,xe2x80x9d must be capable of maintaining a hermetic seal when subjected to the temperatures and pressures associated with retorting.
Although closures for many applications, such as carbonated beverages, are made entirely from plastic, in the past, closures for retortable containers were made from metal or, more recently, composites of metal and plastic, such as polypropylene. Such a composite retortable closure is disclosed in U.S. Pat. No. 4,813,561 (Ochs). In such closures, sealing between the closure and container neck is provided by a bead of sealant, such as plastisol, applied to the metallic portion of the closure. The use of metal in a retortable closure was thought necessary because the high temperatures associated with retorting weakens and distorts plastic. It was thought that unless metal was used to stiffen and stabilize the closure, especially the portion supporting the sealant, the high temperatures and pressure resulting from retorting would result in loss of the hermetic seal.
Consequently, it would be desirable to provide a retortable plastic closure with improved sealing capability.
It is an object of the current invention to provide a retortable plastic closure, especially an all-plastic retortable closure. This and other objects is accomplished in a retortable container system, comprising (i) a container having a neck portion forming an approximately cylindrical inner wall, the upper portion of the inner wall having a diameter d2, (ii) a closure, the closure comprising (i) a generally circular plastic top portion having upper and lower surfaces, and (ii) a generally cylindrical plastic skirt portion extending downwardly from the top portion, the skirt portion having means for securing the closure to the container neck portion, (iii) a seal for sealing the closure to the container. The seal comprises a (i) circumferentially extending ridge integrally formed in the plastic top portion so as to project downwardly from the lower surface thereof, the ridge forming a first structural wall extending downwardly from the lower surface of the plastic top portion, and (ii) a flexible liner bonded to the lower surface of the plastic top portion, a first portion of the flexible liner covering at least the first structural wall so as to form a downwardly extending liner wall, the liner wall having a diameter that is greater than the diameter of the container neck inner wall upper portion, whereby the container neck inner wall compresses the liner wall when the closure is applied to the container.